Field of the Invention
This invention relates to drive systems for saturable variable reluctance electrical machines. In particular, the present invention relates to drive and control systems permitting servomotor performance and characteristics to be achieved from a variable or switched reluctance motor, and also relates to control features useful in self-contained control systems not necessarily comprising a variable reluctance motor, but applicable to a variety of such motors. The invention is especially directed to control systems for motors incorporating the features of co-pending patent application Ser. No. 789,038 entitled "Variable Speed Variable Reluctance Electrical Machines", as well as to control systems for drives incorporating motors having these features.
According to a first aspect of said co-pending application, there is provided a drive system comprising a saturable variable reluctance electrical motor, said motor comprising a stationary or driving member having a plurality of salient driving poles, a magnetizing winding for each driving pole, and a movable or driven member having a plurality of salient driven poles, the number of driven poles being less than the number of driving poles, and a plurality of airgaps, the airgap between each driving pole and a driven pole positioned in alignment therewith being small relative to the dimensions of the poles transverse to said airgap and at least the driven poles being formed so that in operation of the motor magnetic saturation occurs substantially in the region of the mechanically variable interface or overlap between the driving and driven poles, and the extents and dispositions of the driven poles being related to those of the driving poles so that in operation of the motor the force-producing increment of driven member displacement resulting from the mechanical interface or overlap of each driven pole with a driving pole overlaps the force-producing increment of driven member displacement resulting from the overlap of another driven pole with a further driving pole, and the system also comprising driven member position-sensing means for generating at least one signal, the instantaneous value of which is dependent on the position of the driven member, and power supply means including a voltage source or sources connectible across the driving pole windings, said windings being connectible across said source or a said source in a predetermined sequence during driven member displacement and each driving pole winding being thus connectible for a predetermined increment of driven member displacement, and the power supply means also including means for regulating the instantaneous magnitude of the current in a driving pole winding when connected to said source or a said source, said current-regulating means being responsive to the or a said driven member position-dependent signal of the driven-member position-sensing means to regulate said current magnitude so that the instantaneous value of said current set by said regulating means at any position of the driven member within said increment of driven member displacement during which the winding is connectible to said source or a said source relative to its value at any other said position is substantially determined by the instantaneous position of the driven member.
In a rotary construction, said stationary or driving member is a stator and said driving poles are stator poles, said movable or driven member is a rotor and said driven poles are rotor poles, while said driven member displacement is represented by rotation of the rotor.
In another aspect, this co-pending application discloses a saturable variable reluctance electrical machine comprising a stationary or driving member having a plurality of salient driving poles, a winding for each driving pole, a movable or driven member having a plurality of driven poles, the number of driven poles being less than the number of driving poles, the airgap between each driving pole and a driven pole positioned in alignment therewith being small relative to the dimensions of the poles transverse to said airgap and at least the driven poles being formed so that in operation of the machine magnetic saturation occurs substantially in the region of the mechanically variable interface or overlap between the driving and driven poles, the extents and dispositions of the driven poles being related to those of the driving poles so that in operation of the machine the force-producing increment of driven member displacement resulting from the mechanical interface or overlap of each driven pole with a driving pole overlaps the force-producing increment of driven member displacement resulting from the overlap of another driven pole with a further driving pole, each driven pole and each driving pole having edge regions spaced apart in the direction of relative displacement of the driven and driving members, said spacing of said edge regions being substantially constant throughout the extent of the pole in a direction transverse to said direction of relative displacement and each said edge region being defined in said transverse direction of the pole by a succession of edge region portions, each said edge region portion being displaced in said direction of relative displacement with respect to the or each adjacent edge region portion of said edge region, each said edge region portion being advanced in said direction of relative displacement with respect to the preceding edge region portion of each said edge region portion being set back in said direction of relative displacement with respect to the preceding edge region portion so that said edge region is skewed relative to said direction of relative displacement, and the spacing in said direction of relative displacement between the edge region portion at one transverse end of one of said edge regions of the pole and that at the other transverse end of the same edge region being between one quarter of the constant extent of the pole in said direction of relative displacement and a value equal to said extent.
In a rotary construction, said stationary or driving member is a stator and said driving poles are stator poles, said movable or driven member is a rotor and said driven poles are rotor poles, and said driven member displacement is represented by rotation of the rotor, while said transverse direction is a direction parallel to the axis of rotation.